Noob - Please Help

I am a complete noob and I have a couple of questions. I have a linksys WRT54G v3 router and am looking to upgrade to dd-wrt. do I use the full version or the mini version? Also how exactly do I upgrade? Do I have to reset the reset the router first. Any help would be appreciated.

hiya here is the instructions, please remember the wiki is your friend and full of answers

1) Download firmware

go to the DD-WRT homepage at [1] (http://www.dd-wrt.com/)
Read the changelog and all other information files on the download pages. They contain important information!
Note: Use the mini version when upgrading from original Linksys firmware!
If you downloaded a .zip file, then extract the archive.
Confirm good download by comparing the MD5 hash fingerprint of the firmware you downloaded with published Hashes.
2a) Reset to Factory Defaults through the Web GUI
If you forgot the password or IP of your router, proceed to step 2b.

Log into the Web GUI of the router. Type in the address of the router (default 192.168.1.1) into the address bar of your browser.
You will be prompted for username and password. Username is not required (for versions >= 2006-Feb-28, username is root). Enter password (default password is admin) and you should be at the Web Interface of your router.
Click the "Administration" tab.
Click the "Factory Defaults" sub-tab.
Select "Yes".
Click the "Save Settings" button.
A new page will open, click "continue".
2b) Reset to Factory Defaults Using the Reset Button

Press and hold the reset button on the back of the router for 30 seconds. This will clear your NVRAM, the configuration and reset the username/password pair to root/admin.
3) Send in the Firmware!

It is VERY important that you do not interrupt the setup while the router is being flashed/rebooted. Do not turn off the computer, close the web browser, or turn off the router during this process!!!!! I usually just take a step back, and turn my head away so I don't breathe on it for these crucial 2 minutes.
Use Internet Explorer as the Linksys firmware has many incompatibilities with Mozilla Firefox, in particular in the firmware upgrade section (although this is *REALLY* hard to do if you are a Linux user, and can't convince Microsoft to make a version of internet exploder for you).
Again, you should be in the Web GUI of the router. Go there now.
Click the "Administration" tab
Click the "Firmware Upgrade" sub-tab.
Click the "No reset" radio button (works for me, but please double check if "Firmware Defaults" would be better!).
Click the "Browse" button and select the DD-WRT .bin file you extracted in step 1.
Click the "Upgrade" button.
The router will take a few minutes to upload the file, flash the firmware, and then reset.
A new page will open, wait about 5 minutes before clicking "Continue".
If flashed successfully you will now be at the DD-WRT web interface.
4) Reset to factory defaults AGAIN

Repeat step 2a or 2b above. Note: Step 2b (the manual way of clearing the NVRAM) is recommended to make sure the radio gets the correct parameters.
5) Enjoy

It is strongly advised that you enable the "Boot Wait" option under the "Administration" tab. This will help you recover in the future should you flash your router improperly. If you use v23 or higher the "Boot Wait" option is enabled by default.